This invention relates to systems for detecting relative motion between a wave transmitter-receiver and a reflecting surface, and more particularly to detecting relative motion, either parallel or normal to the reflecting surface or both.
It is often desirable to detect relative motion between two objects. Coherent wave systems devised for that purpose have principally been of the doppler type where the frequency shift in the reflected signal received at the transmitter is used to determine the relative velocity between the transmitter-receiver (transceiver) and the reflecting surface. The velocity thus measured is along the radar beam axis. Consequently, if motion parallel to the reflecting surface is desired, it must be computed using a complex system. It is also not possible to measure the extent (distance) of the relative motion or position relative to the reflecting surface. Instead, it is necessary to compute it relative to a starting point as a product of velocity and time.
In any instances it is desirable to detect relative motion parallel to the reflecting surface, and to measure the extent of the motion and/or rate. For example, an aircraft pilot needs to know ground velocity in order to navigate by dead reckoning. Similarly, the captain of a ship needs to know his velocity through the water, and both the pilot and the captain need to know the total distance traveled at a given heading. That is customarily computed from velocity. If the velocity is relative to the water, accurate navigation requires that the velocity of the water relative to the earth also be detected.
There are many applications for relative motion detection besides navigation. For vehicular traffic control, as an example, it is sometimes desirable to know almost instantly the velocity of a vehicle passing a point on the side of the road. Many analogous applications in industrial process control will readily occur to those skilled in the art. The motion to be detected may not always be linear; it may, for example, be the turning of a wheel. In some cases the problem may be to detect any motion, and the extent and/or rate of motion between an object and a reflecting surface, where the object is to be stationary relative to the surface. In still other cases, what is of interest is position alone relative to a reflecting surface. Detected motion and/or position may be used in a servo system to control the motion or maintain the position of the object.